A Stirling engine is an externally heated reciprocating engine. It has a cylinder within which oscillation of a piston or pistons serves to move a working fluid between hot and cold heat exchangers and provide power output.
Heat is generally supplied to one end of the cylinder of the Stirling engine in order to heat the gas inside and drive the working piston. The end of the Stirling engine which is heated is called a heat transfer head and is generally surrounded by an annular heater or burner, which supplies heat to the heat transfer head. The cylinder is generally arranged vertically, with a burner surrounding it to supply heat so that hot exhaust gases from the burner can escape upwards. In order to enhance the transfer of heat to the cylinder of the Stirling engine to increase its efficiency the heat transfer head can be provided with fins to increase-its surface area.